Mechanical Ventilation

Question 1

2 major drawbacks of positive pressure ventilation?

Answer 1

It causes hypotension and barotrauma.

Question 2

Negative pressure ventilators (…personal iron lung-ish things) don’t cause hypotension and barotrauma. Why aren’t they more commonly used?

Answer 2

The tidal volume you can generate is limited.
You can’t control the airway.
(they’re really only used in neuromuscular diseases, and sometimes COPD)

Question 3

You can set a volume or set a pressure with the respirator. Which is preferred for acute respiratory failure?

Answer 3

Volume-cycled, positive pressure ventilation is preferred.

Question 4

Is hypoxemia alone reason to go to mechanical ventilation?

Answer 4

No. Try oxygen first. Mechanical ventilation and/or intubation is indicated when 100% oxygen by face mask is inadequate.

Question 5

5 indications for mechanical ventilation (MV)?

Answer 5

Hypercapnea.
Hypoxemia (but.. it’s not actually that good at fixing it.)
Decrease work of breathing (probs most important).
In shock, to spare CO.
Airway protection

Question 6

Does MV improve gas exchange?

Answer 6

No, not per se. But if you add in PEEP, it may.

Question 7

MV increases length of hospital stay, costs, and complications.

Answer 7

Sure does.

Question 8

Review: Equation for work of breathing?

Answer 8

W = integral ( P deltaV)

Question 9

How can you change pCO2 with a ventilator?

Answer 9

By changing the alveolar ventilation - by adjusting the rate and tidal volume.

Question 10

What’s the deal with peak flow and patient comfort?

Answer 10

Patients are more comfortable with a shorter inspiration, longer expiration - which is achieved with a higher peak flow.
But higher peak flow -> higher pressure, which can be bad)

Question 11

Why does increased peak flow increase airway pressure?

Answer 11

Higher peak flow leads to turbulent flow -> more pressure.

Question 12

How can MV actually improve hypoxia? (it’s not with increased fiO2)

Answer 12

Positive end-expiratory pressure (PEEP) - keeps alveoli open during expiration.
(PEEP allows for lower fiO2, too, which is great)

Question 13

When giving MV to a hypercapnic patient, is normal PCO2 the goal?

Answer 13

No. You don’t want to be too aggressive… Just aim for safe.

Question 14

How does MV improve PCO2?

Answer 14

By increasing (worsening) V/Q due to increased dead space via…
Radial traction on airways.
High pressures divert blood flow -> dead space in zone 1 lung.
Decreased venous return.

Question 15

What’s the first treatment for hypotension associated with MV?

Answer 15

Fluid bolus - get more preload to the heart.

just like in cardiac tamponade… because, similarly, the hyper-inflated lungs are compressing the heart

Question 16

4 adverse effects of MV?

Answer 16

Hypotension.
Barotrauma.
Respiratory distress & auto-PEEP.
Acute lung injury.

Question 17

Complications of barotrauma? (4 things)

Answer 17

Pneumothorax.
Pneumomediastinum.
Pneumopericardium.
Subcutaneous emphysema.

Question 18

What are the two most important values for figuring out the cause of respiratory distress of a patient on MV?

Answer 18

Peak and plateau pressures.

really the difference between them is what you care about

Question 19

What lung function variable(s) is/are reflected in peak pressure?

Answer 19

Both compliance and airflow.

Question 20

How do you measure plateau pressure?

Answer 20

Occlude the airway momentarily -> pressure will plateau.

Question 21

What lung function variable(s) is/are reflected in plateau pressure?

Answer 21

Compliance only.

Question 22

How do you calculate the pressure contributed by airflow?

Answer 22

Peak pressure - plateau pressure.

This will reflect pressure generated by airflow.

Question 23

DDx of MV respiratory distress with unchanged P(peak) - P(plateau)?
(i.e. with normal airflow pressure)

Answer 23

Pulm edema.
Pulm embolus.
PNA.
PTX.
Anxiety, pain.
Auto-PEEP.

Question 24

DDx of MV respiratory distress with wide P(peak) - P(plateau)?
(i.e. with increased airflow pressure)

Answer 24

Something must be blocking airflow:
Endotracheal tube problems.
Tubing kinked
Secretions.
Bronchospasm.

Question 25

What is auto-PEEP?

Physiologic causes?

Answer 25

Pressure due to air trapped by insufficient expiratory time.
Caused by high tidal volumes, Starling resistors.
(must suck harder to generate further breaths… can trigger respiratory distress.)

Question 26

Can MV cause ARDS?

Answer 26

Sure can.

Question 27

How can MV be altered to reduce risk of ARDS?

Answer 27

Use low-stretch MV (lower tidal volumes, plateau pressures).

Ventilate the sickest patients less!

Question 28

4+ aspects monitoring MV?

Answer 28

Clinical: secretions, mental status.
CXR and ABGs.
Daily spontaneous breathing trials (switch off machine while still intubated).
Static compliance (Cstat)

Question 29

What’s static compliance?

Answer 29

Cstat is the change in lung volume divided by change in distending pressure.

Question 30

You really should really really know the equation for static compliance (Cstat).

Answer 30

Cstat = Tidal Volume / (Plateau pressure - PEEP pressure)